Surprising News About Bicycle-Powered Electricity Generators

That hourglass-shaped device is the PowerPac, an energy storage device meant to be powered by a human on a stationary bicycle. Conceived of by South African design firm Ideso, the PowerPac won a Red Dot Design Award in the "Best of the Best" category.

"Our aim was to create an aesthetically pleasing, user-friendly and functional design that marries the fluidity of cycling with dynamic power generation," says Ideso MD, Marc Ruwiel. "It can be used by avid cyclists who can reduce CO2 emissions and generate their own electrical power, while enjoying a good workout at home."

I'm all for people-powered electricity generators, and I would've loved to have one of these during the recent blackout, but something struck me in the copy: "...An average cyclist could fully charge the battery from empty with 80 minutes of cycling and 132Wh of charge/potential energy can be stored in the battery." The "Wh" designation stands for watt-hour, and "132Wh" means you could power a 132-watt device for 1 hour. For 80 minutes of cycling to yield, say, just over two hours of light from a 60-watt bulb sounds like a low yield, doesn't it? My first thought was, can that be right?

I did a little digging, and here's what I found. It turns out hooking a bicycle up to something that directly powers a mechanical device is a fairly efficient way to generate energy. Rig a bicycle up to drive a sewing machine or a hand mixer and you get decent bang for your buck. But the second you get batteries and electricity involved, the efficiency drops way, way off. An article in Low-tech Magazine called "Bike powered electricity generators are not sustainable" explains why:

...Generating electricity is far from the most efficient way to apply pedal power, due to the internal energy losses in the battery, the battery management system, other electronic parts, and the motor/generator. These energy losses add up quickly: 10 to 35 percent in the battery, 10 to 20 percent in the motor/generator and 5 to 15 percent in the converter (which converts direct current to alternate current). The energy loss in the voltage regulator (or DC to DC converter, which prevents you from blowing up the battery) is about 25 percent. This means that the total energy loss in a pedal powered generator will be 42 to 67.5 percent....

And it even turns out that the bicycle itself has mechanical inefficiencies that suck up more energy:

The second problem with the present approach to pedal power is that it uses a traditional bicycle on a training stand instead of a pedal powered machine built from scratch —as was the case at the end of the 19th century....

...This approach is considerably less efficient. One reason is the use of a so-called friction drive—the rear bicycle wheel acts upon the small roller of the motor/generator. While chain and belt drives (used in late 19th century pedal powered machines) have an efficiency of up to 98 percent, a friction drive is only 80 to 90 percent efficient (and wears much faster). This energy loss should be added to the 42 to 67.5 percent efficiency loss calculated above, which rises to 48 to 73.5 percent. Low tyre pressure will further decrease efficiency.

...There is also energy loss in the bicycle itself: your pedals are not attached to the rear wheel itself. You turn a sprocket, which turns a chain, which turns a sprocket, which turns the rear wheel. So, on top of the efficiency loss of the friction drive should be added the efficiency loss of a chain drive (plus the energy loss in the derailleur, if your bike has one).

To be clear, I'm not listing these facts to pooh-pooh Ideso's design. They're trying to get the PowerPac into production, and for those off-the grid, inefficient juice is better than no juice at all. But I was surprised to learn of the inefficiencies of pedal power, and I'm hoping that once interested designers become aware of the problems, they'll then figure out ways to solve them.

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19 Comments

Get rid of the friction and scale it up. Just chain right to a DC motor to use as a generator or make the bike wheel itself that flywheel with magnets on it spinning by coils of copper.
http://www.youtube.com/playlist?list=PLy8wksQ9r7SdnmPT6VkiIbDB3s9wBiG0n

I'd like to point out that the frictional losses in the bike system itself are incredibly small, on the order of .1 W, especially if you hold the bike up by something other than the wheel (aka, a bike stand). So that's not a significant factor.
That being said, yes, overall this is not the most efficient way to generate electricy, and I don't think that's the point. This is to be used by people who already have bikes and want to generate some electricity.
Also you should consider what type of efficiency you're talking about. Here there may only be a ~40%-70% work to electricity efficiency, but that work is human exercise. So in order to make a little more electricity, you have to, oh no, burn a few more calories and get some exercise (which is, by the way, good for you...)

I wonder if the system efficiency could be improved by charging up capacitors (which have extremely low internal resistance-I.R ), instead of the batteries directly. Then use the energy stored in the capacitors to trickle charge batteries with a lower charge (C) rate, thereby negating the need to have expensive, low (but still much higher I.R than a capacitor) internal resistance batteries in the system?
I read recently that Mazda's i-Eloop regenerative braking technology is using a circuit design leveraging this idea to cut down the alternator load on some of their vehicles, thus increasing their fuel efficiency.
What a great time to be alive!
Tally Ho!
Jesiah.

Hi Guys,
I have found this post really interesting and brilliantly insightful. I am a student in my final year at Brunel University London studying industrial design. I have chosen to take on a bief which deals very closely with these issues for my major project.
I am currently developing a modular generator for use in areas of energy poverty, globally.
The idea is to create a fixed magnet generator which can then be altered locally using available materials and technologies to hook it up to a number of kinetic inputs.
I am primarily looking at Wind and pedal power as they already use rotary motion and i feel as though i can come up with some solutions for these within the time frame that i have.
I am aiming to create systems that can at least charge a mobile phone due to the rising importance of communication on the developing world.
It would be great to hear your thoughts on the project. And if you had any advice when working within these areas.
Thanks
Milo

crayons: define your "natural cycle". Does it include very regular ice ages, slightly less regular antarctic jungle forests, methane clathrates in northern seas and the fact that coal and petroleum were trees and algae at some point in the past?
We surely return a lot of CO2 and methane into atmosphere, the same carbon that living organisms actively bound for the last billion years or so. But for all we know the richer in carbon our atmosphere is, the greener our planet gets. Warm climate means wet and mild climate, more atmospheric carbon means more food for plants and algae. Remember, last time we had a global warming (holocene thermal maximum, right after the last ice age), we lost the polar ice cap and a significant share of Greenland's glaciers, but also we had green Sahara, wet Africa and people sprouting all over the Earth. Ice ages themselves and harsh, distinct seasons became possible because of the carbon-depleted atmosphere.

crayons - I believe the carbon footprint from food is from the actual production of the food (tractors, combines, etc) and shipment of food (trucks, etc).
That is why on the link that wr provided, an apple grown in your backyard has 0 grams of carbon versus an imported apple is 150 grams.
Meats have a higher footprint because because of the large amount of feed needed to produce the meat.

wr > are you just trying to jack people up?
It's tough to tell these days whats a joke and what is real opinion.
I am pretty sure the main difference between a gram of carbon from humans eating food and a gram of carbon from burning gasoline or coal is that the carbon in gasoline and coal is not part of a natural cycle.... ie: it comes from material buried underground, the carbon has not be taken out of the current atmosphere > therefore all emissions are 100% net increase.
Whereas food (plants) are taking carbon in from the atmosphere to grow, then this same carbon is returned to the atmosphere when the plant is consumed or rots > therefore no net increase in carbon to the atmosphere.
Am I wrong?
That's the difference right?

That's an easy one. I couldn't find the original research (it was british and it was published _some_ years ago, good luck finding it), and i am not crazy enough to repeat it single handedly, breaking down an average meal into discrete components and calculating individual footprints per calory. BUT! Thanks to David McCandless we have a nice web app which you can use to estimate the price of your nasty cycling habbit, in dead baby seals of course:
http://visualization.geblogs.com/visualization/co2/#/food_asparagus_local

I looked at DIY version of this a long time ago and concluded it was way too much effort, expense and complication, so making a product of it is an idea that I think has great potential. My thoughts are that if it is specifically for charging from a bicycle it should probably incorporate the bike stand- you need the mechanical connection to keep the bike on the roller. My other thought is that it would be significantly better value if it had a 'universal' mechanical input that could be hookup up to a variety of human powered devices and probably a gearbox to facilitate that. almost anyone can DIY some really basic mechanical inputs- but almost no-one can build one of these, or even afford the constituent parts as discreet products.
RE the other debate that is emerging here- I hope it is not contentious to suggest that where the input fuel is food, as with all renewable resources efficiency is comparatively unimportant. there is a qualitative difference between food and petrol, though I appreciate that some sort of equivalency may be drawn on the basis of bioethanol production, or the consumption of non-renewables incurred during food production.

Love the design language on this device, it's definitely cool and dynamic. One question I would pose is that of cost. The incorporation of flutes to the hourglass shape would appear, to me, to really complicate any traditional tooling one would use for mass production. Is the plan to use a "production" type FDM machine for all the housings? Otherwise, all I can picture is a bunch of parting lines ($$$)!

Jared - I think having some jacks on your device would be very helpful. Instead of charging "a" battery, I would rather charge the batteries to the many small electical (phones, etc) when on the trainer.
wr - I'd like to see the data behind your claim.
I commute to work about 100 miles/week. If a "normal" diet is 2000 calories/day, to commute on the bike, there is no way that I need more than an additional 300-500 calories/day.
So you need to calculate the footprint of only the additional calories, not the total. I'm going to eat whether I ride a bike or not.
At 100 miles, that is 2 gallons/week a scooter will burn. In addition to teh footprint of making a 300 pound scotter verus a 25 pound bike.
Then on top of that, I would also assume a healthy life has a smaller footprint than an unhealthy life. Less medical resourse, etc. I'm reaching, but if you want to look at the big picture, look at the big picture and have evidence to back a claim. My opinion is no better or worse than yours.

Hi guys,
I am one of the lead designers from Ideso.
Thank you for your constructive criticism. We always welcome discussion of our work and think Core77 is a great platform for that.
Just to clarify a few points.
Human electricity generation from cycling has been around for a long time. What we proposed was a unit that allowed for storage of this energy and a removable section that could be placed anywhere in the house for use when power is required, eg. charging an electronic device or the powering of a small light (3W LED etc).
During this year's Design Indaba in Cape Town, we displayed a working prototype of the concept. We rapid prototyped the housing, used a small permanent magnet DC generator, a 12V battery for storage and an invertor for current conversion.
This public display was a great platform to get people on the bike to generate their own energy, as well as test our prototype. We gathered a lot of great information/data from this. With regards to efficiency, we were experiencing around 70% for the whole system.
We are aware of the inherent losses throughout the system and see this as a challenge for us as designers to come up with various solutions to address this problem.
While the original idea was a purely conceptual in-house project, we now feel that there is potential to take this forward as a side project. We have some great photo's, including the development of the prototype if you would like us to share.
Let me know if you have any other questions etc.
Thanks
Jared

Perhaps, you'll be even more surprised to learn that driving an average SUV leaves a smaller carbon footprint than walking, and riding a modern scooter is much greener than cycling. Our bodies are fairly inefficient in converting energy/CO2 emissions into work, and our food production chains, especially meat production, generate helluva greenhouse gases, both directly (livestock emits crazy amounts of methane) and indirectly (fuel and electricity spent). So it seems a good idea, catching and storing some of the energy you'd waste anyway while exercising, and cycling/running/walking is good for your health, but there's nothing green in it. Wanna go green - buy a scooter.

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